Surface Chemistry-Tyndall Effect

The Tyndall Effect is the scattering of light passing through a particular medium. Mediums may vary from a Solution to Colloidal or Suspension. Tyndall Effect is seen in the particles when the particle diameter ranges from 40 and 900 nanometres. 

Tyndall Effect definition

As the light passes through the medium, the suspension particles present in the liquid scatter and reflect the light, enabling the ray or beam to be visible on the opposite side. This whole phenomenon is known as the Tyndall Effect. 

The Tyndall Effect depends on the medium. Sometimes, it depends on the frequency or intensity of light passing through the medium. Medium, which shows the Tyndall Effect is only visible in Colloidal and Suspension medium. It is not visible in solutions. The solution has a fine layer of particles that doesn’t allow light to pass through it. Colloidal mediums have space between the particles, allowing light to pass through them. The amount of light scattered also depends on the frequency and density of light. Suspension particles do not show this effect as the particles settle down quickly. 

A common example of this effect is the visible Sun rays in a forest. Due to the high number of trees in the woods, 90% of the rays don’t reach the ground. The thick canopy of trees ceases them. Only 10% or less light comes down to the ground. 

Solution medium

Solution medium has the finest particles. They are homogenous, tiny, and have little or almost no space between them. That’s why they don’t show the Tyndall Effect. We can easily see it in the Sugar solution as the sugar dissolves in the water and doesn’t show the Tyndall Effect. The particle sizes are not large enough to show this effect. 

Colloidal medium

The size of a particle in a Colloidal medium is 1 nanometre to 1 micrometre. They are heterogeneous and have large molecules. The particles in the medium cannot be separated by filtration. There are various classes in colloids which include different phases and mediums. When they mix, we get different combinations like Sol, Gel, Foam, Aerosol etc. When studied under a microscope, the colloids move in rapid and random motion. This motion is called the Brownian motion of particles. 

Suspension medium

The suspension medium has a high range of particles. They are bigger than the colloidal particles, and that’s why they do not show the Tyndall Effect. We can find the Suspension medium in sand and gravel. If we dip sand in water, the particles settle down in the water after some time and allow the light to pass through this medium. The Tyndall phenomenon is observed when the light scatters through the particles. It is why this medium doesn’t show the Tyndall Effect.

The different classes of Colloidal medium are: 

• When the Dispersed phase is Solid, and the Dispersion medium is Solid, it is called Solid Sol. 
• If the Dispersed phase is Solid and the Dispersion medium is Liquid, it is called Sol. 
• When the Dispersed phase is Solid, and the Dispersion medium is Gas, it is called Aerosol. 
• When the Dispersed phase is Liquid, and the Dispersion medium is Solid, it is called Solid Sol.
• When the Dispersed phase is Liquid, and the Dispersion medium is Liquid, it is called Emulsion.
• If the Dispersed phase is Liquid and the Dispersion medium is Gas, it is called Aerosol. 
• When the Dispersed phase is Gas and Dispersion medium is Solid, it is called Solid Sol. 
• When the Dispersed phase is Gas, and the Dispersion medium is Liquid, it is called Foam. 

So, these are the different classes in the Colloidal medium. 

Conclusion

The Tyndall Effect is the scattering of light due to the particles present in the medium. The Solution medium doesn’t show the Tyndall Effect as the particles are very fine. In contrast, the Colloidal particles have a size of particles from 40 to 900 nanometre, and that’s why they show the Tyndall Effect. The Suspension particles have a size higher than this range. They settle quickly in the medium, and thus the light doesn’t scatter or reflect; therefore, this medium also doesn’t show the Tyndall Effect. 

So, the Tyndall Effect is only shown by the Colloidal particles. They have the accurate size of creating this phenomenon.